1. Field of the Invention
The invention relates to a reference current generation technique. Particularly, the invention relates to a reference current generation circuit suitable for applying in a chip.
2. Description of Related Art
FIG. 1 is a schematic diagram of a conventional current source circuit. Referring to FIG. 1, the conventional current source circuit 100 includes a bandgap voltage generator 102, an operational amplifier 104, an external resistor Rext, an N-type transistor M1 and P-type transistors Q1-Q3. A positive input terminal of the operational amplifier 104 is coupled to the bandgap voltage generator 102, a negative input terminal thereof is coupled to a source of the N-type transistor M1, and an output terminal of the operational amplifier 104 is coupled to a gate of the N-type transistor M1. The external resistor Rext is coupled between the source of the N-type transistor M1 and ground. Moreover, a gate of the P-type transistor Q1 is coupled to a drain thereof, the drain of the P-type transistor Q1 is coupled to a drain of the N-type transistor M1, and a source of the P-type transistor Q1 is coupled to a power voltage VDD. In addition, gates of the P-type transistors Q2 and Q3 are coupled to the gate of the P-type transistor Q1, and sources of the P-type transistors Q2 and Q3 are coupled to the power voltage VDD.
As shown in FIG. 1, when a reference current non-related to temperature, process and reference voltage is required to be generated in internal of a chip, according to a conventional method, the bandgap voltage generator 102 is used to generate an accurate reference voltage VBG, and the operational amplifier 104 duplicates such voltage to the external resistor Rext of the chip through a negative feedback manner, so as to generate the required reference current on the channel of the P-type transistor Q1. The P-type transistors Q2 and Q3 are used to duplicate the reference current flowing through the P-type transistor Q1, and output the duplicated reference current through the drains thereof. Although the accurate reference current can be generated according to the conventional technique, external pins of the chip have to be increased, and the external resistor Rext occupies a large space, which may increase a manufacturing cost, and is not economic effective.